Most people should sign up for Medicare Part A, which covers in-patient and hospital care, as soon as they are eligible; it’s generally free.

If you’re still working and you get health insurance from your employer, however, you can delay enrolling in Part B, which covers doctors’ visits and outpatient care.

The monthly premium is $104.90 for most people in 2015. It’s more if your income is higher than $85,000 if single or $170,000 if married filing jointly

If you’re already collecting Social Security when you turn 65, you automatically will be enrolled in parts A and B, and the Part B premium will be deducted from your benefits each month.

Keep in mind that although you are eligible for Medicare at 65, your full retirement age for Social Security is 66.

If you’re still working at 65 and decide to delay enrolling in Part B, you’ll have eight months to do so after you lose your employer coverage.

If you miss that deadline, you’ll have to wait until the next Part B open-enrollment period (from January 1 to March 31), and your monthly premium will increase by 10 percent for each 12-month period you delay.

You can no longer make contributions to a health savings account after you sign up for Medicare Part A or Part B.

So if you’re still working and have a high-deductible health insurance policy and an HSA through your employer, you may want to delay signing up for Medicare so that you can continue to contribute to your HSA.

That’s especially true if your employer pitches in some money to the account.

But you may not be able to delay enrolling in Part A if you’ve already signed up for Social Security benefits or if your employer has fewer than 20 employees. In that case, Medicare will be your primary coverage.